Unraveling Bridging-Oxygen-Driven Ultrafast Amorphization in Superionic Oxyhalide Conductors via in Situ Synchrotron...

The energy- and time-consuming mechanochemical synthesis of high-performance solid electrolytes (SEs) remains a critical bottleneck for the scaling of all-solid-state batteries. Despite the recognition that oxygen incorporation in structure serves as a viable strategy to develop high-performance halide SEs, systematic investigations into how oxygen in structure modulates synthesis kinetics, local structure, and ion transport are scarce. Herein, we report the synthesis of amorphous oxyhalide NaTaOCl₄ as a model system, achieved via minute-scale ball milling, a dramatic improvement over the multi-day synthesis of conventional NaTaCl₆. Complementary structural characterizations and ab initio molecular dynamics (AIMD) simulations demonstrate that, low-coordinated bridging-oxygen-dominated Ta-O-Cl environments induce substantial lattice distortions, enabling ultrafast amorphization. Time-resolved in situ synchrotron x-ray scattering experiments reveal distinct reaction pathways: NaTaOCl₄ undergoes rapid fragmentation of precursors into metastable intermediates followed by bridging-oxygen-driven amorphous formation, whereas NaTaCl₆ experiences a moderate crystallization process prior to prolonged amorphization. By extending this design to a series of mixed‑anion oxyhalides, we establish a universal rapid synthesis strategy. For instance, NaTaO_0.5Cl₅ exhibits high ionic conductivities of 3.39 mS cm^-1 after only 30 min of ball-milling. This work establishes a strategy that employs oxygen as a structural bridging-agent to develop high-conductivity SEs and provides atomic-scale insights into ultrafast mechanochemical reaction.